Compositions and methods for energy storage device electrodes

ABSTRACT

An energy storage device can include a cathode, an anode, and a separator between the cathode and the anode, where the anode and/or electrode includes an electrode film having a super-fibrillized binder material and carbon. The electrode film can have a reduced quantity of the binder material while maintaining desired mechanical and/or electrical properties. A process for fabricating the electrode film may include a fibrillization process using reduced speed and/or increased process pressure such that fibrillization of the binder material can be increased. The electrode film may include an electrical conductivity promoting additive to facilitate decreased equivalent series resistance performance. Increasing fibrillization of the binder material may facilitate formation of thinner electrode films, such as dry electrode films.

STATEMENT REGARDING FEDERALLY SPONSORED R&D

This invention was made with government support under DEFC2605NT42403awarded by the United States Department of Energy. The government hascertain rights in the invention.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

Field

The present invention relates to energy storage devices, particularly tocompositions of and methods for electrodes of energy storage devices.

Description of the Related Art

Various types of energy storage devices can be used to power electronicdevices, including for example, capacitors, batteries, capacitor-batteryhybrids and/or fuel cells. An energy storage device, such as a lithiumion capacitor, having an improved electrode composition can facilitateimproved capacitor electrical performance.

SUMMARY

For purposes of summarizing the invention and the advantages achievedover the prior art, certain objects and advantages of the invention aredescribed herein. Not all such objects or advantages may be achieved inany particular embodiment of the invention. Thus, for example, thoseskilled in the art will recognize that the invention may be embodied orcarried out in a manner that achieves or optimizes one advantage orgroup of advantages as taught herein without necessarily achieving otherobjects or advantages as may be taught or suggested herein.

In a first aspect, an electrode for use in an energy storage devicecomprising a free-standing dry electrode film, is provided herein,comprising dry carbon particles; and dry super-fibrillized binderparticles; and a current collector.

In an embodiment of the first aspect, the dry electrode film has athickness of about 50 μm to about 120 μm. In an embodiment of the firstaspect, the electrode is an anode. In an embodiment of the first aspect,the free-standing dry electrode film further comprises a conductivecarbon. In an embodiment of the first aspect, the electrode filmcomprises the conductive carbon in about 1% to about 5% by mass. In anembodiment of the first aspect, the electrode is in ionic contact withan electrolyte comprising a lithium salt. In an embodiment of the firstaspect, the electrolyte is further in ionic contact with a cathode. Inan embodiment of the first aspect, the dry super-fibrillized binderparticles comprise about 3 wt % to about 7 wt % of the free-standing dryelectrode film. In an embodiment of the first aspect, a lithium ioncapacitor is provided, comprising the electrode.

In a second aspect, a method for fabricating a dry energy storage deviceelectrode film is provided, comprising forming a first dry electrodemixture comprising dry carbon particles and dry fibrillizable binderparticles; super-fibrillizing the binder in the dry electrode filmmixture to form a super-fibrillized matrix within the electrode filmmixture; and calendaring the super-fibrillized electrode film mixture toform a free-standing super-fibrillized electrode film.

In an embodiment of the second aspect, wherein the method is a drymethod in which substantially no processing additives are used. In anembodiment of the second aspect, the method further comprises contactingthe free-standing electrode film with a current collector to form afirst electrode. In an embodiment of the second aspect, the methodfurther comprises forming a second electrode, and inserting a separatorbetween the first electrode and the second electrode. In an embodimentof the second aspect, the first electrode is an anode. In an embodimentof the second aspect, the free-standing dry electrode film has athickness of about 50 μm to about 120 μm. In an embodiment of the secondaspect, the dry super-fibrillized binder particles comprise about 3 wt %to about 7 wt % of the super-fibrillized matrix. In an embodiment of thesecond aspect, forming the first mixture further comprises addingconductive carbon particles to the first mixture. In an embodiment ofthe second aspect, the first mixture comprises the conductive carbonparticles in about 1% to about 5% by mass. In an embodiment of thesecond aspect, super-fibrillizing the binder comprises: fibrillizing thebinder in the dry electrode film mixture to form a first fibrillizedmatrix; destructuring the first fibrillized matrix to form a powderedmixture of carbon particles and fibrillized binder particles; andfibrillizing the powdered mixture to form a second fibrillized matrix,wherein the second fibrillized matrix comprises the super-fibrillizedmatrix.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure are described with reference to the drawings of certainembodiments, which are intended to illustrate certain embodiments andnot to limit the invention.

FIG. 1 shows a side cross-sectional schematic view of an example of anenergy storage device, according to one embodiment.

FIG. 2 is a process flow diagram showing an example of a process forfabricating an electrode film.

FIG. 3 is a table listing respective equivalent series resistanceperformance of lithium ion capacitor cells with anodes comprisingdifferent types of electrical conductivity promoting additives.

FIG. 4 is a process flow diagram showing an example of a process forfabricating an electrode film with reduced thickness.

FIG. 5A is a schematic diagram of an unwinder machine for the electrodefilm calendar line.

FIG. 5B is a more detailed schematic view of a portion of the unwindermachine shown in FIG. 5A.

FIGS. 6A and 6B depict SEM images of electrode films prepared by a dryelectrode process known in the art (FIG. 6A) and by a dry electrodeprocess implementing super-fibrillized binder (FIG. 6B), respectively.

FIG. 7 provides tabular data for various embodiments of lithium ioncapacitors having an anode created by the methods provided herein.

DETAILED DESCRIPTION

Although certain embodiments and examples are described below, those ofskill in the art will appreciate that the invention extends beyond thespecifically disclosed embodiments and/or uses and obvious modificationsand equivalents thereof. Thus, it is intended that the scope of theinvention herein disclosed should not be limited by any particularembodiments described below.

In some embodiments, an energy storage device, such as a lithium ioncapacitor (LiC), with improved electrical and/or mechanical performancecharacteristics is provided. In some embodiments, the device can have anelectrode comprising an improved electrode film composition, which inturn can provide improved electrical and/or mechanical performance. Insome embodiments, the electrode can be an anode and/or cathode.

Embodiments herein can comprise mixtures of materials for electrodefilms, electrode films, electrodes, energy storage devices, and relatedmethods, having increased fibrillization of binder material, relative toconventional processes, or “super-fibrillization” as described furtherand defined herein. A number of electrical and/or mechanical performanceadvantages may be realized by increasing binder fibrillization.

For instance, binder adherence and thus film strength may be increasedby increasing binder fibrillization. Such embodiments can allowfabrication of thinner films using the same or less amount of binderthan a comparable film with binder that is not as fibrillized. Usingthinner films can be beneficial for dry electrode film technology, whichconventionally have had thicker films than wet electrode processes, dueto the free-standing nature of the dry electrode films and otherfactors. Additionally, any decrease in the percentage of binder byweight (“binder loading”) in proportion to some of the other materials,such as conductive materials, in an electrode film has electricalperformance benefits. For example, use of super-fibrillized binder andreduced binder loading in an electrode film can also decrease theundesirable Electrical Series Resistance (ESR) in a device using thefilm, relative to conventional films with conventionally fibrillizedbinder.

In some embodiments, an electrode film of the anode and/or cathode maycomprise a fibrillizable binder material and another electrode material,such as carbon. The electrode film can have a reduced quantity of thebinder material while maintaining desired mechanical properties. Suchdesired mechanical properties may relate to, for example, the mechanicalproperties needed for one or more steps of a fabrication process for anenergy storage device. For example, when an electrode is manufacturedusing a dry fabrication process, a freestanding electrode film canadvantageously provide sufficient stability to be rolled, handled, etc.,prior to adhering the film to a current collector. Further, increasingfibrillization of the binder material may advantageously facilitateformation of thinner electrode films which can withstand the calendarline tension. In some embodiments, electrode films comprising anincreased number of fibrils, greater fibril surface area, and/or longerfibrils may have a reduced thickness while demonstrating sufficientmechanical strength to maintain desired film integrity duringfabrication of the film.

A process for fabricating the electrode film may comprise afibrillization process using reduced speed and/or increased processpressure, such that fibrillization of the binder material can beincreased, relative to previously known conventional electrode filmfibrillization processes. For example, increased fibrillization mayprovide an increased number of fibrils, greater fibril surface area,and/or longer fibrils from the binder material such that desiredmechanical properties can be maintained while using a reduced quantityof binder material, relative to previously known conventional electrodefilm fibrillization processes. It is believed that such increased numberof fibrils, greater fibril surface area, and/or longer fibrils allow amore efficient matrix structure in an electrode film, thus providing oneor more advantages described herein. In some embodiments, the moreefficient matrix structure can result in an electrode film withincreased tensile strength in length, resistance to shear, compressive,and/or twisting stress, decreased film thickness, increased filmdensity, and reduced binder loading, relative to previous dry electrodetechniques. In certain embodiments, the electrode film is afree-standing electrode film having a reduced binder loading as providedherein.

In certain embodiments, the electrode film is a free-standing electrodefilm comprising a super-fibrillized binder particles and carbonparticles. As provided herein, super-fibrillized binder particles arebinder particles fabricated according to the processes herein, such asprocess 200 and/or 400, including binder particles that are fibrillized,reduced, and then re-fibrillized; binder particles that are fibrillizedat a higher pressure, lower speed, lower feed rate, and/or longerduration than conventional fibrillization techniques; super-fibrillizedbinder particles can be structurally defined based upon the number offibrils, fibril surface area, and/or fibril length, all of which areincreased relative to conventional binder fibrillization techniques. Asprovided herein, a super-fibrillized matrix is the structure formed bythe constituents of an electrode film mixture in which the binderparticles have been super-fibrillized, which have a level of adhesionwith each other, due to the fibrillization process, but which have notyet been compressed into an electrode film, for example, as depicted inFIG. 6B.

In some embodiments, the super-fibrillized binder particles arecharacterized by a greatest dimension of less than about 3 microns (μm),less than about 2 μm, less than about 1 μm, less than about 0.5 μm, lessthan about 0.3 μm, less than about 0.1 μm, less than about 0.05 μm, lessthan about 0.03 μm, less than about 0.01 μm, or values therebetween, forexample, about 0.01 to 3 μm, about 0.03 to 2 μm, about 0.05 to 1 μm, orabout 0.1 to 0.3 μm. In further embodiments, super-fibrillized matrixcomprises carbon particles having at least 10%, at least 20%, at least30%, at least 40%, at least 50%, at least 60%, at least 70%, at least80%, at least 90%, at least 95%, or at least 99% surface area in contactwith binder particles, or a range of values therebetween. In someembodiments, the super-fibrillized binder particles are present in anelectrode film in at least twice the number compared to conventional dryprocess electrode film of equivalent binder mass.

Conventional dry electrode films formed using a dry process from dryparticle electrode film mixtures fabricated using standard techniques,with conventionally fibrillized binder generally are characterized by athickness of greater than or equal to about 120 μm for anodes, andgreater than or equal to about 80 μm for cathodes. The differences inthicknesses between these two types of dry electrodes are attributed tothe following: anode electrode films may be more difficult to compressthan cathode electrode films, for example due at least in part todifficulty in compressing carbon material of the anode, such as comparedto activated carbon of the cathode electrode film. Generally, suchconventional cathode films can range from about 80 μm to about 10,000μm, and such anode films can range from about 120 μm to about 10,000 μm.

In some embodiments, increasing fibrillization of the binder material,relative to conventional dry electrode processes, may facilitateformation of thinner electrode films. Advantageously, thinner electrodefilms can be used in lithium ion capacitors occupying less volume. Insome embodiments, super-fibrillization of the binder material mayfacilitate formation of cathode electrode films with a thickness of lessthan or equal to about 80 μm, 60 μm, or even 50 μm, while maintaining orincreasing structural integrity and/or electrical performance, relativeto otherwise similar conventional dry electrode films withconventionally fibrillized dry-binder material. In some embodiments, anelectrode film fabricated using one or more processes described hereincan have a thickness less than or equal to about 120 μm, 80 μm, 60 μm,and even about 50 μm, where the electrode is optionally an anode. Insome embodiments, increasing fibrillization of the binder material mayfacilitate formation of anode electrode films with a thickness less than120 microns (μm). In some embodiments, increasing fibrillization of thebinder material may facilitate formation of thinner electrode films,such as electrode films of a thickness less than 120 microns (μm), 80μm, 60 μm, less than 50 μm, less than 40 μm, or less than 30 μm,including anode electrode films less than 120 μm, and even lower, andcathode electrode films less than 120 μm, 80 μm, and even lower. In someembodiments, thinner electrode films can provide improved lithium ioncapacitor power capabilities. In some embodiments, an anode for use in alithium ion capacitor comprises an electrode film having a thickness ofabout 40 μm to about 120 μm, about 50 μm to about 120 μm, about 50 μm toabout 80 μm, about 60 μm to about 100 μm, or about 80 μm to about 120μm. In some embodiments, a cathode for use in a lithium ion capacitorcomprises an electrode film having a thickness of about 40 μm to about80 μm, about 40 μm to about 70 μm, about 50 μm to about 80 μm, about orabout 50 μm to about 70 μm.

In some embodiments, the electrode film comprises an electricalconductivity promoting additive to facilitate decreased equivalentseries resistance performance. The additive may be a carbon black and/orgraphite. In some embodiments, the electrode film comprises a reducedquantity of the binder material and an increased quantity of one or moreelectrical conductivity promoting additives, relative to previouslyknown conventional electrode films, such that embodiments of the presentelectrode films can demonstrate decreased equivalent series resistancewhile maintaining desired mechanical properties.

A lithium ion capacitor comprising one or more electrodes having anelectrode film composition described herein may advantageouslydemonstrate reduced equivalent series resistance, thereby providing acapacitor with increased power density, relative to previously knownconventional electrode films. In some embodiments, improved equivalentseries resistance performance may facilitate reduced heat generation,thereby reducing or avoiding thermal dissipation of lithium ioncapacitors comprising conventional electrode films. In some embodiments,lithium ion capacitors comprising one or more electrodes havingelectrode film compositions described herein may be cheaper tofabricate. In some embodiments, lithium ion capacitors comprising one ormore electrode compositions described herein can have a variety ofshapes, including prismatic, cylindrical and/or button shaped. In someembodiments, a lithium ion capacitor comprising an electrolyte asdescribed herein can be used to power hybrid electric vehicles (HEV),plug-in hybrid electric vehicles (PHEV), and/or electric vehicles (EV)vehicles.

It will be understood that although the electrodes and energy storagedevices herein may be described within a context of lithium ioncapacitors, the embodiments can be implemented with any of a number ofenergy storage devices and systems, such as one or more batteries,capacitors, capacitor-battery hybrids, fuel cells, combinations thereof,and the like, with or without lithium. In some embodiments, theelectrode is a cathode or an anode configured for use in anultracapacitor, a lithium ion capacitor, or a lithium ion battery. Inpreferred embodiments, the electrode is an anode configured for use in alithium ion capacitor.

FIG. 1 shows a side cross-sectional schematic view of an example of anenergy storage device 100. The energy storage device 100 may be alithium ion capacitor. Of course, it should be realized that otherenergy storage devices are within the scope of the invention, and caninclude batteries, capacitor-battery hybrids, and/or fuel cells. Theenergy storage device 100 can have a first electrode 102, a secondelectrode 104, and a separator 106 positioned between the firstelectrode 102 and second electrode 104. For example, the first electrode102 and the second electrode 104 may be placed adjacent to respectiveopposing surfaces of the separator 106. The first electrode 102 maycomprise a cathode and the second electrode 104 may comprise an anode,or vice versa. The energy storage device 100 may include an electrolyte122 to facilitate ionic communication between the electrodes 102, 104 ofthe energy storage device 100. For example, the electrolyte 122 may bein contact with the first electrode 102, the second electrode 104 andthe separator 106. The electrolyte 122, the first electrode 102, thesecond electrode 104, and the separator 106 may be received within anenergy storage device housing 120. For example, the energy storagedevice housing 120 may be sealed subsequent to insertion of the firstelectrode 102, the second electrode 104 and the separator 106, andimpregnation of the energy storage device 100 with the electrolyte 122,such that the first electrode 102, the second electrode 104, theseparator 106, and the electrolyte 122 may be physically sealed from anenvironment external to the housing. It will be understood that energystorage device 100 is shown as a dual-electrode, dual layer device, butother types can be implemented, such as single-layer electrodes.

The energy storage device 100 can include any of a number of differenttypes of electrolyte 122. For example, device 100 can include a lithiumion capacitor electrolyte, which can include a lithium source, such as alithium salt, and a solvent, such as an organic solvent. In someembodiments, a lithium salt can include lithium hexafluorophosphate(LiPF₆), lithium tetrafluoroborate (LiBF₄), lithium perchlorate(LiClO₄), lithium bis(trifluoromethansulfonyl)imide (LiN(SO₂CF₃)₂),lithium trifluoromethansulfonate (LiSO₃CF₃), combinations thereof,and/or the like. In some embodiments, a lithium ion capacitorelectrolyte solvent can include one or more ethers and/or esters. Forexample, a lithium ion capacitor electrolyte solvent may compriseethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate(DEC), ethyl methyl carbonate (EMC), vinyl carbonate (VC), propylenecarbonate (PC), combinations thereof, and/or the like. For example, theelectrolyte may comprise LiPF₆, ethylene carbonate, propylene carbonateand diethyl carbonate.

The separator 106 can be configured to electrically insulate twoelectrodes adjacent to opposing sides of the separator 106, such as thefirst electrode 102 and the second electrode 104, while permitting ioniccommunication between the two adjacent electrodes. The separator 106 cancomprise a variety of porous electrically insulating materials. In someembodiments, the separator 106 can comprise a polymeric material. Forexample, the separator 106 can comprise a cellulosic material (e.g.,paper), a polyethylene (PE) material, a polypropylene (PP) material,and/or a polyethylene and polypropylene material.

As shown in FIG. 1, the first electrode 102 and the second electrode 104include a first current collector 108, and a second current collector110, respectively. The first current collector 108 and the secondcurrent collector 110 may facilitate electrical coupling between thecorresponding electrode and an external circuit (not shown). The firstcurrent collector 108 and/or the second current collector 110 cancomprise one or more electrically conductive materials, and/or havevarious shapes and/or sizes configured to facilitate transfer ofelectrical charges between the corresponding electrode and a terminalfor coupling the energy storage device 100 with an external terminal,including an external electrical circuit. For example, a currentcollector can include a metallic material, such as a material comprisingaluminum, nickel, copper, silver, alloys thereof, and/or the like. Forexample, the first current collector 108 and/or the second currentcollector 110 can comprise an aluminum foil having a rectangular orsubstantially rectangular shape and can be dimensioned to providedesired transfer of electrical charges between the correspondingelectrode and an external electrical circuit (e.g., via a currentcollector plate and/or another energy storage device componentconfigured to provide electrical communication between the electrodesand the external electrical circuit).

The first electrode 102 may have a first electrode film 112 (e.g., anupper electrode film) on a first surface of the first current collector108 (e.g., on a top surface of the first current collector 108) and asecond electrode film 114 (e.g., a lower electrode film) on a secondopposing surface of the first current collector 108 (e.g., on a bottomsurface of the first current collector 108). Similarly, the secondelectrode 104 may have a first electrode film 116 (e.g., an upperelectrode film) on a first surface of the second current collector 110(e.g., on a top surface of the second current collector 110), and asecond electrode film 118 on a second opposing surface of the secondcurrent collector 110 (e.g., on a bottom surface of the second currentcollector 110). For example, the first surface of the second currentcollector 110 may face the second surface of the first current collector108, such that the separator 106 is adjacent to the second electrodefilm 114 of the first electrode 102 and the first electrode film 116 ofthe second electrode 104.

The electrode films 112, 114, 116 and/or 118 can have a variety ofsuitable shapes, sizes, and/or thicknesses. For example, the electrodefilms can have a thickness of about 30 microns (μm) to about 250microns, including about 100 microns to about 250 microns.

In some embodiments, an electrode film, such as one or more of electrodefilms 112, 114, 116 and/or 118, can have a mixture comprising bindermaterial and carbon. In some embodiments, the electrode film can includeone or more additives, including electrical conductivity promotingadditives. In some embodiments, the electrode film of a lithium ioncapacitor cathode can comprise an electrode film mixture comprising oneor more carbon based electroactive components, including for example aporous carbon material. In some embodiments, the porous carbon materialof the cathode comprises activated carbon. For example, the electrodefilm of the cathode and can include a binder material, activated carbonand an electrical conductivity promoting additive. In some embodiments,the electrode film of a lithium ion capacitor anode comprises anelectrode film mixture comprising carbon configured to reversiblyintercalate lithium ions. In some embodiments, the lithium intercalatingcarbon is graphite. For example, the electrode film of the anode caninclude a binder material, graphite and an electrical conductivitypromoting additive.

In some embodiments, the binder material can include one or morefibrillizable binder components. For example, a process for forming anelectrode film can include fibrillizing the fibrillizable bindercomponent such that the electrode film comprises fibrillized binder. Insome embodiments, the fibrillized binder comprises super-fibrillizedbinder particles as provided herein. The binder component may befibrillized to provide a plurality of fibrils, the fibrils desiredmechanical support for one or more other components of the film. Forexample, a matrix, lattice and/or web of fibrils can be formed toprovide desired mechanical structure for the electrode film. Forexample, a cathode and/or an anode of a lithium ion capacitor caninclude one or more electrode films comprising one or more fibrillizedbinder components. In some embodiments, a binder component can includeone or more of a variety of suitable fibrillizable polymeric materials,such as polytetrafluoroethylene (PTFE), ultra-high molecular weightpolyethylene (UHMWPE), and/or other suitable fibrillizable materials,used alone or in combination.

In some embodiments, the electrode film comprises a reduced quantity ofthe binder material by weight, relative to previously known conventionaldry electrode films, while maintaining desired mechanical properties. Insome embodiments, the electrode film comprises about 1 weight % to about10 weight %, about 3 weight % to about 15 weight %, about 3 weight % toabout 10 weight %, about 3 weight % to about 8 weight %, about 3 weight% to about 7 weight %, about 3 weight % to about 6 weight %, or about 3weight % to about 5 weight %, of the binder material. In furtherembodiments, the electrode film is an anode comprising binder materialin about 4 wt % to about 7 wt %, for example about 5 wt % to about 6 wt% or about 6.5 wt % to about 8 wt %. In some embodiments, the electrodefilm is a cathode comprising binder material in about 7 wt % to about 11wt %, for example about 8 wt % to about 10 wt %, along with activatedcarbon. In some embodiments, the electrode film, such as the anode film,can comprise binder material that is less than about 4%, or even 3% byweight, for example, between about 0.5% and 4% by weight, 1% and 4% byweight, 0.5% and 3% by weight, or 1% and 3% by weight. In someembodiments, the electrode film comprising a reduced quantity of bindercan maintain desired resistance to a tensile, shear, compressive, and/ortwisting stress.

In some embodiments, the electrode film comprises a reduced quantity ofbinder material, relative to other materials in the film, facilitatingthe use of an increased quantity of the electrical conductivitypromoting additive, improving electrical performance. For example, ananode implementing such an embodiment can demonstrate improvedequivalent series resistance, while maintaining or even increasingdesired mechanical properties. In some embodiments, particular types ofelectrical conductivity promoting additive can be included in theelectrode film to provide desired electrical performance. For example,the electrode film comprising a reduced quantity of binder material maydemonstrate desired resistance to a tensile, shear, compressive, and/ortwisting stress, while demonstrating improved equivalent seriesresistance, thereby facilitating fabrication of an energy storagedevice, such as a lithium ion capacitor having increased power density,relative to previously known conventional energy storage devices ofotherwise comparable structure.

In some embodiments, the electrical conductivity promoting additivecomprises a conductive carbon. In some embodiments, the conductivecarbon comprises one or more types of carbon black and/or graphite. Insome embodiments, the one or more types of carbon black comprisecommercially available Ketjenblack® from Akzo Nobvel N.V., C-NERGY™Super C65 from Imerys Graphite & Carbon, Ltd., Super P® from ImerysGraphite & Carbon, Ltd., BP2000® from Cabot Corp., and/or LITX® 50 fromCabot Corp. In some embodiments, the one or more types of graphitecomprise commercially available ABG1010 from Superior Graphite Co.,and/or ABG1005 from Superior Graphite Co. For example, an anodeelectrode film of a lithium ion capacitor may include one or more of theelectrical conductivity promoting additives described herein. In someembodiments, the conductive carbon can be about 1 weight % to about 10weight % of the electrode film mixture, including about 1 weight % toabout 8 weight %, or about 1 weight % to about 5 weight %. In someembodiments, including a conductive carbon, as provided herein, in theelectrode film can result in an ESR improvement of about 5% relative toan energy storage device that does not include the conductive carbon. Infurther embodiments, the conductive carbon is characterized by a surfacearea of 10-100 m²/g, for example 20-50 m²/g, and/or a particle size of0.1 to 10 μm. In still further embodiments, the conductive carbon ischaracterized by a particle size of about 0.1 μm to about 0.5 μm, orabout 10 μm. In some embodiments, a lithium ion capacitor including ananode fabricated by the methods provided herein can be characterized byan ESR of about 0.1 mΩ to about 10 mΩ for example, about 0.5 mΩ to about5 mΩ or about 1.5 mΩ to about 3.5 mΩ.

In some embodiments, one or more electrode films described herein can befabricated using a dry fabrication process. As used herein, a dryfabrication process can refer to a process in which no or substantiallyno solvents are used in the formation of an electrode film. For example,components of the electrode film may comprise dry particles. The dryparticles for forming the electrode film may be combined to provide adry particles electrode film mixture. In some embodiments, the electrodefilm may be formed from the dry particles electrode film mixture usingthe dry fabrication process such that weight percentages of thecomponents of the electrode film and weight percentages of thecomponents of the dry particles electrode film mixture are similar orthe same. In some embodiments, the electrode film formed from the dryparticles electrode film mixture using the dry fabrication process maybe free or substantially free from any processing solvents, and solventresidues resulting therefrom. In some embodiments, the electrode filmformed from the dry particles electrode film mixture using the dryfabrication process can be cleaner and/or structurally stronger, andthereby providing improved electrochemical and/or mechanicalperformance. In some embodiments, the electrode films are free-standingdry particle electrode films formed using the dry process from the dryparticles mixture. In some embodiments, a free-standing dry electrodefilm, consists essentially or consists of dry carbon particles and drysuper-fibrillized binder particles. In some embodiments, only a singlebinder is used to form the free-standing dry electrode film, such as asingle fibrillizable binder, such as PTFE.

In some embodiments, the energy storage device is not a battery.

FIG. 2 is a process flow diagram showing an example of a process 200 forfabricating an electrode film, according to some embodiments. In someembodiments, the process 200 for fabricating an electrode film is a dryprocess, where no liquids or solvents are used such that the resultingelectrode film is free or substantially free of any liquids, solvents,and resulting residues. In block 202, an electrode film mixture isformed comprising carbon particles and a binder material. Optionally oneor more electrical conductivity promoting additives can be combined. Insome embodiments, the electrode film mixture is a dry particles mixture.In some embodiments, the binder material comprises one or morefibrillizable polymers, such as polytetrafluoroethylene (PTFE) andultra-high molecular weight polyethylene (UHMWPE). In some embodiments,the binder material consists or consists essentially of one type ofpolymer, such as PTFE. In some embodiments, the electrical conductivitypromoting additive can be one or more conductive carbons. For example,the conductive carbon can include one or more types of carbon blackand/or graphite described herein.

In block 204, the binder in the electrode film mixture can besuper-fibrillized to form a super-fibrillized matrix. Thesuper-fibrillization process can be performed using a conventionalfibrillization process, with reduced speed and/or increased processpressure. For example, the super-fibrillization process may be performedwith reduced speed and/or reduced pressure relative to that described inU.S. Patent Publication No. 2015/0072234. In some embodiments, thesuper-fibrillization process can be a mechanical shearing process. Forexample, mechanical shearing force can be applied to the binder materialto manipulate the binder material such that a plurality of fibrils canbe formed from the binder material. In some embodiments, the mechanicalshearing process comprises a blending and/or a milling process. Forexample, the speed with which particles of the electrode film mixtureare fed or cycled through the blender and/or mill may be reduced duringthe super-fibrillization process. Reducing the speed with whichparticles of the electrode film mixture are cycled through the blenderand/or mill may increase the duration in which the particles of theelectrode film mixture are cycled once within the process chamber of theblender and/or mill. In some embodiments, increased duration of thecycle can increase fibrillization of the binder material, providingsuper-fibrillization of the mixture. In some embodiments, the speed withwhich the particles of the electrode film mixture are cycled within theblender and/or mill is selected such that the duration in which theparticles are cycled once within the process chamber is about 1.2 timesto about 3 times that of conventional dry electrode processes. Forexample, the duration of a blending and/or a milling process for aconventional dry process can be about 1 minute. In some embodiments, theduration of blending and/or milling is about 2 minutes, about 3 minutes,about 4 minutes, about 5 minutes, about 7 minutes, or about 10 minutes.The feed rate of blending and/or milling can be reduced relative toconventional dry electrode processing procedures, for example, by abouthalf. In some embodiments, the feed rate of blending and/or milling isabout 10% of the rated machine feed rate, about 20% of the rated machinefeed rate, about 30% of the rated machine feed rate, about 40% of therated machine feed rate, about 50% of the rated machine feed rate, about60% of the rated machine feed rate, about 70% of the rated machine feedrate, about 80% of the rated machine feed rate, or about 90% of therated machine feed rate. In some embodiments, an electrode film isprovided, wherein the electrode film is prepared by a process comprisingblending and/or milling a dry mixture of carbon particles and binder forabout 2 to about 5 minutes.

In some embodiments, a continuous mixing process can be used. In suchembodiments, the duration of blending and/or milling can be inverselyrelated to the feed rate. Thus, in such embodiments, feed rate can bereduced compared to a conventional dry fibrillization process toincrease the duration of blending and/or milling. In some embodiments,reducing the feed rate to half will double blending and/or millingduration. For example, the feed rate for a conventional dry process oncertain machinery can be about 50-60 kg/hr. Thus, in some embodiments, asuper-fibillized binder or matrix as provided herein can be produced ata feed rate of about 25-30 kg/hr on the same machinery. Generally, thefeed rate is dependent on the milling machinery, and can be adjustedbased on the machine operating parameters in view of guidance providedherein. In further embodiments, equipment with larger channels can beused to increase the duration of blending and/or milling. When a batchblending and/or milling process is used, the duration can be increasedsimply by blending and/or milling for a longer time.

In some embodiments, the process pressure within the blender and/or millduring the fibrillization process may be increased to providesuper-fibrillization. In some embodiments, increased process pressurefacilitates increased shearing force exerted upon the binder material,thereby increasing fibrillization of the binder material. In someembodiments, the process pressure during the super-fibrillizationprocess can be selected such that the shearing force exerted upon thebinder material is about 1.2 times to about 3 times that of conventionaldry electrode fibrillization processes.

A super-fibrillization process comprising reduced speed and/or increasedprocess pressure may facilitate increased fibrillization of the bindermaterial, such that an increased number of fibrils, greater fibrilsurface area, and/or longer fibrils being formed from the bindermaterial. In some embodiments, the reduced speed and/or increasedprocess pressure facilitates increased formation of fibrils such that areduced quantity of binder material can be used to form the electrodefilm having the desired resistance to a tensile, shear, compressive,and/or twisting stress. For example, the reduced speed and/or increasedprocess pressure may facilitate formation of sufficient fibrils suchthat desired mechanical support can be provided for one or more othercomponents of the film while using a reduced quantity of bindermaterial. In some embodiments, the combining step of block 202 andfibrillization step of block 204 may be one or substantially onecontinuous step.

In certain embodiments, the super-fibrillization provided by block 204can be performed by repeating a conventional fibrillization processestwo or more times on the same material. In such embodiments, afibrillized matrix can be formed through a first fibrillization process.The fibrillized matrix may then be reduced in size, for example, to forma first powdered electrode film mixture. For example, block 204 cancomprise the step of destructing the first fibrillized electrode filmmixture. Destructuring the electrode film can comprise passing thefibrillized electrode film mixture through a strainer, sifter, mesh,riddle, screen and/or sieve. The destructured fibrillized electrode filmmixture can then be super-fibrillized, by subjecting it to a secondfibrillization step as provided herein. The second fibrillization stepcan be a fibrillization process performed with reduced speed and/orincreased process pressure as provided herein. The second fibrillizationstep can result in a second powdered electrode film mixture. The secondpowdered electrode film mixture can then be subjected to furtheriterations of the step(s) of block 204, or in turn to the step(s) ofblock 206. In some embodiments, the second (or additional)fibrillization step(s) provides an electrode film mixture with increasedfibrillization and one or more advantages resulting therefrom, asprovided herein. Thus, the super-fibrillization of the binder in block204 can occur after one, two, three, or more fibrillization sub-steps.The end result, is that block 204 provides a super-fibrillized matrix,and/or super-fibrillized binder particles, as provided herein.

In block 206, the fibrillized electrode film mixture can be calendaredin a calendar apparatus to form a free-standing super-fibrillizedelectrode film. A calendar apparatus is well known in the art, andgenerally includes a pair of calendar rolls between which raw material,such as an electrode film mixture is fed, to form an electrode film. Insome embodiments, an electrode film can be formed in a first calendaringstep, without additional calendaring steps, to form a film at a desiredminimum thickness, as described further herein. In some embodiments, thecalendared mixture forms a free-standing dry particles film free orsubstantially free from any liquids, solvents, and resulting residuetherefrom. In some embodiments, the electrode film is an anode electrodefilm. In some embodiments, the electrode film is a cathode electrodefilm. In some embodiments, the super-fibrillized electrode film mixturecan be calendared under selected conditions. For example, in furtherembodiments, calendaring can be performed at a temperature of 10 to 300°C., at a pressure of 5 to 150 kilo newton force. The calendar can be asize selected for a particular application, but generally can have adiameter in the range of 5 to 80 cm.

FIG. 3 is a table listing respective equivalent series resistanceperformance of lithium ion capacitor cells including anodes comprisingdifferent types of electrical conductivity promoting additives. Thetable lists the type of electrical conductivity promoting additiveincluded in each of the capacitor anodes, and the correspondingequivalent series resistance performance is listed as a percentageimprovement relative to a lithium ion capacitor without any of theelectrical conductivity promoting additives. The electrical conductivitypromoting additive tested included mesoporous carbon, and various typesof conductive carbons. As shown in the table of FIG. 3, shows thatlithium ion capacitors with an anode comprising certain types ofconductive carbons demonstrated improved equivalent series resistanceperformance, while lithium ion capacitors with an anode comprisingmesoporous carbon did not demonstrate significant improvement inequivalent series resistance performance. For example, lithium ioncapacitors with an anode comprising certain types of conductive carbonsdemonstrated 5% or more improvement in equivalent series resistanceperformance.

Tests also showed that lithium ion capacitors with an anode comprisingmetal powders such as silver (Ag) powder, nickel (Ni) powder, or copper(Cu) powder did not demonstrate significant improvement in equivalentseries resistance performance.

FIG. 4 is a process flow diagram showing an example of a process 400 forfabricating an electrode film with a reduced thickness, according tosome embodiments. In some embodiments, the electrode film can be acathode electrode film. In some embodiments, the electrode film can bean anode electrode film. In some embodiments, the process 400 forfabricating an electrode film is a dry process, where no liquids orsolvents are used such that the resulting electrode film is free orsubstantially free of any liquids, solvents, and resulting residues. Insome embodiments, the process 400 can be applied to form electrodes ofultracapacitors, batteries, and/or lithium ion capacitors.

In block 402, components of an electrode film mixture comprising abinder material and one or more electrical conductivity promotingadditives can be combined. In some embodiments, the electrode filmmixture is a dry particles mixture. The binder material may comprise oneor more fibrillizable polymers, such as polytetrafluoroethylene (PTFE)and ultra-high molecular weight polyethylene (UHMWPE). In someembodiments, the binder material consists or consists essentially of onetype of polymer, such as PTFE. In some embodiments, the electricalconductivity promoting additive can be one or more conductive carbons.For example, the conductive carbon can include one or more types ofcarbon black and/or graphite described herein.

In block 404, the electrode film mixture can be fibrillized to formfibrils from the binder material. The fibrillization process can beperformed with reduced speed and/or increased process pressure. Thereduced speed and/or increased process pressure may facilitate increasedformation of fibrils such that a reduced quantity of binder material canbe used to form the electrode film having the desired resistance to atensile, shear, compressive, and/or twisting stress. As describedherein, in some embodiments, the fibrillization process can bemechanical shearing process, for example, comprising a blending and/or amilling process. In some embodiments, the speed with which particles ofthe electrode film mixture are cycled through the blender and/or millmay be reduced during the fibrillization process. In some embodiments,the process pressure within the blender and/or mill during thefibrillization process may be increased. In some embodiments, thecombining step of block 402 and fibrillization step of block 404 may beone or substantially one continuous step. The reduced speed and/orincreased process pressure can allow an electrode film with theaforementioned greater strength to be manufactured at a thickness lowerthan previously possible, such as lower than 120 μm or otherwisedescribed herein, either through a single, higher pressure calendaringprocess (in a single step), or through multiple calendaring steps, forexample, where the film is unwound, and subsequently re-calendared, oneor more times after an initial calendaring step.

In certain embodiments, block 404 can comprise the step of reducing insize, for example, destructuring, the fibrillized electrode filmmixture, and re-fibrillizing it, such as that described with referenceto block 204 in FIG. 2. In block 406, the fibrillized electrode filmmixture can be calendared to form a first electrode film. In block 408,the first electrode film can be unwound. For example, the firstelectrode film can be run through an unwinder, such as the unwindershown in FIGS. 5A and 5B described below. In block 410, the unwoundelectrode film can be recalendared at least once. In some embodiments,the electrode film can be recalendared two or more times to form anelectrode film having a reduced thickness, such as a thickness of about50 μm, or less, or the other reduced thicknesses described herein. Insome embodiments, the electrode film with the reduced thickness is afree-standing dry particles electrode film which can demonstrate desiredresistance to a tensile, shear, compressive, and/or twisting stress. Forexample, an electrode film, such as an anode electrode film of a lithiumion capacitor subjected to one pass through the calendaring line mayhave a thickness of about 120 μm. The electrode film implemented withthe increased fibrillization described herein can have increasedstrength to allow the calendared electrode film to be unwound, and runthrough the calendar line, one or more additional, to reach a thicknessbelow about 120 μm. For example, the film can be calendared a secondtime to a lower thickness, such as a thickness of about or below 80 μm.The recalendared anode electrode film may be unwound and run through thecalendar line a third time to form an electrode film having a thicknessof about 50 μm.

In some embodiments, an electrode film having a thickness less than 80μm, or other reduced thicknesses described herein, relative toconventional electrode film thicknesses, can be fabricated by running anelectrode film mixture with super-fibrillized binder only once through acalendar line. For example, the calendar may exert sufficient pressureupon the electrode film mixture such that a thickness of less than 80 μmcan be achieved by calendaring the mixture only once, due to the higherstrength of the film due to its higher fibrillization. Achievingelectrode films having the desired reduced thickness by passing theelectrode film mixture through the calendar machine only once canprovide a cheaper and/or higher speed fabrication process.

FIG. 5A is a schematic diagram of an embodiment of an unwinder machinefor the electrode film calendar line. FIG. 5B is a more detailedschematic view of a portion of the unwinder machine shown in FIG. 5A.The equipment shown in FIGS. 5A and 5B can be used to implement therecalendaring step 410 of FIG. 4. For example, in the illustratedembodiment, a free-standing dry electrode film (shown in FIG. 5B as“unwinding material) is unwound and re-calendered in the pair of rollersshown. It will be understood that similar calendaring equipment such asthe rollers shown in FIGS. 5A and 5B can be implemented to receive andcompress a dry electrode mixture and initially form the free-standingdry electrode film in a first calendaring step, such as step 206 in FIG.2, and step 410 of FIG. 4, or other embodiments.

FIG. 6A and FIG. 6B show SEM images of dry electrode films matrices.FIG. 6A shows an SEM image of a dry electrode film matrix fabricated bya conventional dry electrode process. FIG. 6B shows a dry electrode filmmatrix fabricated according to a super-fibrillization process, such asprocess 200 or others described herein. The electrode film in FIG. 6Acontains 8% of binder and has a thickness of 80 μm. The electrode filmin FIG. 6B contains 6.5% of binder, has a thickness of 50 μm. Theelectrode film in FIG. 6B was fabricated from an electrode film mixturethat was subjected to a second milling process. As can be seen bycomparison of FIG. 6A and FIG. 6B, the dry electrode film matrix of FIG.6B is characterized by increased binder fibrillization. Specifically, inFIG. 6B, an increased number of fibrils are present. In FIG. 6A, asubstantial portion of the carbon particles (labeled as such) have freesurfaces, while in FIG. 6B, fibrillized binder coats a substantiallyincreased surface area of the carbon particles. Generally, the binderdepicted in FIG. 6B has a greater surface area for the same mass, andmakes contact with a greater surface area of the carbon particles, thanthe binder in FIG. 6A. The binder in FIG. 6B is an example of asuper-fibrillized binder as provided herein.

FIG. 7 provides tabular data regarding binder loading, film thicknesses,cell capacitance, and ESR for various embodiments of lithium ioncapacitors having an anode created by the methods provided herein.

Although this invention has been disclosed in the context of certainembodiments and examples, it will be understood by those skilled in theart that the invention extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses of theinvention and obvious modifications and equivalents thereof. Inaddition, while several variations of the embodiments of the inventionhave been shown and described in detail, other modifications, which arewithin the scope of this invention, will be readily apparent to those ofskill in the art based upon this disclosure. It is also contemplatedthat various combinations or sub-combinations of the specific featuresand aspects of the embodiments may be made and still fall within thescope of the invention. It should be understood that various featuresand aspects of the disclosed embodiments can be combined with, orsubstituted for, one another in order to form varying modes of theembodiments of the disclosed invention. Thus, it is intended that thescope of the invention herein disclosed should not be limited by theparticular embodiments described above.

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the devices and methodsdisclosed herein.

What is claimed is:
 1. A method for fabricating a dry energy storage device electrode film comprising: forming a first dry electrode film mixture comprising dry carbon particles and dry fibrillizable binder particles; super-fibrillizing the dry fibrillizable binder particles in the dry electrode film mixture to form a super-fibrillized matrix within the electrode film mixture, wherein super-fibrillizing the dry fibrillizable binder particles comprises: fibrillizing the dry fibrillizable binder particles in the dry electrode film mixture to form a first fibrillized matrix; destructuring the first fibrillized matrix to form a powdered mixture of carbon particles and fibrillized binder particles; and fibrillizing the powdered mixture to form a super-fibrillized electrode film mixture comprising a second fibrillized matrix, wherein the second fibrillized matrix comprises the super-fibrillized matrix; and calendering the super-fibrillized electrode film mixture to form a free-standing super-fibrillized electrode film.
 2. The method of claim 1, wherein the method is a dry method in which substantially no processing additives are used.
 3. The method of claim 1, further comprising contacting the free-standing super-fibrillized electrode film with a current collector to form a first electrode.
 4. The method of claim 3, further comprising forming a second electrode, and inserting a separator between the first electrode and the second electrode.
 5. The method of claim 3, wherein the first electrode is an anode.
 6. The method of claim 1, wherein calendering comprises compressing the free-standing super-fibrillized electrode film to a thickness of about 50 μm to about 120 μm.
 7. The method of claim 6, wherein calendering to the thickness of about 50 μm to about 120 μm comprises a single calendering step.
 8. The method of claim 1, wherein the super-fibrillized matrix comprises dry super-fibrillized binder particles, and wherein the dry super-fibrillized binder particles comprise about 5 wt % to about 7 wt % of the super-fibrillized matrix.
 9. The method of claim 1, wherein forming the first dry electrode film mixture further comprises adding conductive carbon particles to the first dry electrode film mixture.
 10. The method of claim 9, wherein the first dry electrode film mixture comprises the conductive carbon particles in about 1% to about 5% by mass.
 11. The method of claim 4, further comprising inserting the first electrode, separator and second electrode into a housing with an electrolyte to form an energy storage device.
 12. The method of claim 11, wherein the energy stroage device is a battery.
 13. The method of claim 1, wherein the dry fibrillizable binder particles comprise a binder selected from the group consisting of polytetrafluoroethylene (PTFE), ultra-high molecular weight polyethylene (UHMWPE), and combinations thereof. 